Method for sensing cardiac contractile function using a lead insertable motion sensor

ABSTRACT

Systems and methods for detecting and measuring cardiac contractile function of a heart using an acceleration sensor unit inserted within the heart, such as within a vein of the cardiac wall are disclosed. The systems and methods involve detecting the occurrence of electrical events within the patient&#39;s heart by inserting and positioning an implantable lead having an electrode near a cardiac wall as well as detecting mechanical events within the patient&#39;s heart by then inserting and positioning a cardiac motion sensor unit through the inner lumen of the implantable lead. Furthermore, the systems and methods do not require dedicated leads and may be used with preexisting implantable leads.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/004,686, filed Dec. 5, 2001, now issued as U.S. Pat. No. 6,980,866,and is a divisional of U.S. patent application Ser. No. 10/008,397, fileDec. 6, 2001, now issued as U.S. Pat. No. 6,993,389, said applicationincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to cardiac sensing devices. Morespecifically, the present invention relates to insertable accelerationsensor units that provide signals representative of cardiac mechanicalactivity.

BACKGROUND

Implantable cardiac sensing and stimulating devices are generally usedto manage a variety of heart arrhythmias and conduction systemblockages. Heart arrhythmias, such as bradycardia and tachycardia, oftenprevent the heart from pumping an adequate amount of blood. When thebody does not receive enough oxygen-carrying blood, symptoms such asfatigue, shortness of breath, dizziness, and unconsciousness may occur.Furthermore, conduction system blockages in the heart cause slow,asynchronous contractions that reduce the pumping efficiency and lowercardiac output. Implantable cardiac sensing and stimulating devices mustbe capable of detecting such arrhythmias and decreased pumpingefficiency due to conduction system blockages, and the implantabledevice should respond to the detected arrhythmia or low pumpingefficiency by providing therapeutic electrical stimulation.

Accurate measurement of cardiac activity is needed to deliver effectivetherapy by an implantable cardiac sensing and stimulating device. Manycardiac sensing and stimulating devices that detect and distinguishamong cardiac arrhythmias monitor heart rate, which is usuallyaccomplished by measuring cardiac electrical activity. Furthermore, thefunctions of the conduction system and synchronization of cardiac wallcontractions are assessed by measuring and analyzing cardiac electricalactivity. However, electrical activity is not a sufficiently accuraterepresentation of the mechanical function of the heart. Thus, using onlyelectrodes to sense cardiac mechanical activity can have somedisadvantages in some circumstances.

Some implantable cardiac sensing and stimulating devices includeimplantable leads with built-in accelerometers to measure cardiacmechanical movement representative of cardiac contractile function.However, built-in accelerometers typically require a dedicatedimplantable lead, which tends to be bulky and hard to handle.Furthermore, these conventional leads with built-in accelerometers aretoo large to fit within a vein of a cardiac wall and require invasiveinstallation procedures.

Thus, it is desirable to provide an improved sensing method and systemfor accurately detecting and monitoring cardiac mechanical activities.Further, it is desirable to provide an improved sensing method andsystem that has the ability to be implanted without a dedicated lead,such as within a preexisting implantable lead that may be positionedwithin a vein of a cardiac wall.

SUMMARY

As embodied and broadly described herein, the present invention relatesto a method for detecting and measuring cardiac contractile functionsusing a signal representative of cardiac wall acceleration provided byan acceleration sensor unit. The method involves introducing theacceleration sensor unit into a vein of the cardiac wall and positioningthe sensor so that it responds to the acceleration of the cardiac walland provides a signal representative of the cardiac wall acceleration.The method further involves connecting the acceleration sensor unit toan electronic device.

Moreover, the present invention also relates to another method fordetecting and measuring cardiac contractile functions using a signalrepresentative of cardiac wall acceleration provided by an accelerationsensor. This method involves inserting a guide element along the innerlumen of an implantable lead. The method also involves introducing theimplantable lead into a vein of the cardiac wall. The method furtherinvolves positioning the implantable lead within the vein using theguide element and then removing the guide element from the inner lumenof the implantable lead. Finally, the method involves inserting theacceleration sensor unit along the inner lumen of the implantable lead.

In another embodiment, the present invention relates to a method forcreating an acceleration sensor. This method involves providing animplantable lead and inserting a cardiac motion sensor along the innerlumen of the implantable lead. This method also involves positioning thecardiac motion sensor within the lumen of the implantable lead so thatthe cardiac motion sensor remains mobile along the longitudinal axis ofthe implantable lead.

Further, the present invention also relates to a system for detectingand measuring cardiac contractile functions. This system includes anacceleration sensing means disposed at the cardiac wall for providing asignal representative of acceleration of the cardiac wall. This systemalso includes a conductor means molded into an elongated insulator bodyfor transmitting a signal representative of acceleration of the cardiacwall from the acceleration sensing means to the electronic sensingmeans. This system further includes a connector means for electricallylinking the conductor means to the electronic sensing means.

The present invention also relates to another system for detecting andmeasuring cardiac contractile functions. This system includes anacceleration sensing device disposed at the cardiac wall for providing asignal representative of acceleration of the cardiac wall. The systemalso includes a conductor device molded into an insulated elongate bodyfor transmitting a signal representative of acceleration of the cardiacwall from the acceleration sensing device to the electronic device. Thissystem further includes a connector device for electrically linking theconductor device to the electronic device.

Advantages of the invention will be set forth in part in the descriptionwhich follows or may be learned by practice of the invention. It is tobe understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the invention, as claimed.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation of a typical human heart withacceleration sensor units in accordance with embodiments of the presentinvention;

FIG. 2 depicts an acceleration sensor unit in accordance with anembodiment of the present invention;

FIG. 3 illustrates an implantable lead incorporating a guide element andan acceleration sensor unit in accordance with an embodiment of thepresent invention;

FIG. 4 is a flow chart representing an exemplary method into which anembodiment of the present invention may be incorporated.

DETAILED DESCRIPTION

Various embodiments of the present invention will be described in detailwith reference to the drawings, wherein like reference numeralsrepresent like parts and assemblies through the several views. Referenceto various embodiments does not limit the scope of the invention, whichis limited only by the scope of the claims attached hereto.

Embodiments of the present invention allow detection and measurement ofcardiac contractile functions by an acceleration sensor unit insertedwithin the heart, such as within a vein of the cardiac wall. Theseembodiments also provide systems and methods that may be used withoutrequiring a dedicated lead for the acceleration sensor. Further, theseembodiments provide systems and methods that may be used withpreexisting leads. Certain of these embodiments also provide systems andmethods that may be removed from implantable leads without disturbingthe position of the implantable lead within the heart 100.

FIG. 1 is a schematic representation of a typical human heart withacceleration sensor units in accordance with embodiments of the presentinvention. In FIG. 1, the heart 100 comprises the upper heart chambers,the right atrium area 106 and left atrium area 102, and the lower heartchambers, the right ventricle area 108 and left ventricle area 104. Thecoronary sinus 110 extends from the opening in the right atrium 106laterally around the atria to form the great cardiac vein that extendsfurther inferiorly into branches of the great cardiac vein. Anelectronic device 22 having leads 24, 26 is implanted in a human body(not shown) with portions of the implantable leads 24 and 26 insertedinto the heart 100 and/or veins of the heart 100. The device 22 is usedto detect and analyze electrical cardiac signals and signals indicativeof cardiac wall acceleration produced by the heart 100 and to provideelectrical energy to the heart 100 under certain predeterminedconditions to treat arrhythmias or conduction system blockages. Asshown, the electronic device 22 may be an implantable cardiacresynchronization device for establishing synchronization of ventricularwall contractions, such as for patients with a left bundle branchblockage.

The implantable leads 24 and 26 comprise elongate bodies, both having aproximal end, 32 and 36 respectively, and a distal end, 35 and 38respectively. The implantable leads 24 and 26 further include one ormore pacing/sensing electrodes 50, 52 respectively and/or one or moreacceleration sensor units 46, 44. The implantable lead 26 is passedthrough a vein into the right atrium chamber 106 of the heart 100, intothe coronary sinus 110 and then inferiorly in the great cardiac vein ina basal region to extend the electrode 52 located at the distal end 38onto the cardiac wall alongside the left atrium chamber 102 of the heart100. In an alternative embodiment, the implantable lead 26 may beextended further into the coronary sinus 110 and anterior and/or lateralveins extending therefrom to extend the electrode 52 located at thedistal end 38 onto the cardiac wall alongside the left ventricle chamber104 of the heart 100. In one embodiment, the implantable lead 26 isfixed in place by a distal fixation mechanism 70 comprising a pluralityof fixation tines well known in the art. When the implantable lead 26 ispositioned within the coronary sinus 110, an acceleration sensor unit 44is passed through the inner lumen 28 of the implantable lead 26 toextend the cardiac motion sensor 42, such as an accelerometer, of theacceleration sensor unit 44 alongside preferably either the leftventricle chamber 104 or left atrium chamber 102 of the heart 100. Theacceleration sensor unit 44 may be removed from the inner lumen 28 ofthe implantable lead 26 without removing the implantable lead 26 fromthe coronary sinus 110 of the heart 100.

In an additional embodiment, the implantable lead 24 is passed into theright atrium chamber 106 of the heart 100 and through the tricuspidvalve into the right ventricle 108 where the electrode 50, located atthe distal end 35, is fixed in place in the interventricular septum by adistal attachment mechanism 62. The distal attachment mechanism 62 maybe a wire shaped into a helical cork-screw like projection, a pluralityof fixation tines projecting away from the peripheral surface of theimplantable lead 24, or other structures for attaching the lead 24. Suchdistal attachment mechanisms are well known in the art and are intendedto embed the distal end of the lead 24 in the tissue of the heart. Whenthe implantable lead 24 is fixed in place, an acceleration sensor unit46 is passed through the inner lumen 20 of the implantable lead 24 toextend the cardiac motion sensor 40 located at the distal end of theacceleration sensor unit 46 to the interventricular septum. Theacceleration sensor unit 46 may be later removed from the inner lumen 20of the implantable lead 24, if necessary, without removing theimplantable lead 24 from the interventricular septum of the heart 100.

The implantable device 22 may detect electrical events as well asmechanical events within the heart 100. The electrodes 50, 52 placedinto the heart 100, including the electrode in the coronary sinus veinbranch 110, sense the naturally occurring depolarization of the cells asthe electrical wave travels past the electrode 50, 52 down the surfaceof the heart 100 from the atrium area to the ventricle area. Theacceleration sensor units 44, 46 inserted through the inner lumens 20,28 of the implantable leads 24, 26 sense the cardiac contractilefunctions by providing a signal indicative of cardiac wall acceleration.

The illustrated types and locations of implantable leads 24, 26,electrodes 50, 52 and acceleration sensor units 44, 46 are merelyexemplary. It will be understood that one or more other types ofendocardial and epicardial leads, electrodes and acceleration sensorunits located in or about the right and left chambers of the heart 100as well as the coronary sinus 110 can be substituted for thoseillustrated in FIG. 1 described above.

FIG. 2 illustrates an example of an acceleration sensor unit inaccordance with the present invention. In FIG. 2, the accelerationsensor unit 44 comprises a cardiac motion sensor 42 and a connector 45coupled together by an elongate body 41. The elongate body 41 comprisestwo electrical conductors 43, 47 encompassed by an insulator 49extending longitudinally. The electrical conductors 43, 47 electricallyconnect the cardiac motion sensor 42 located at the distal end of theacceleration sensor unit 44 with the connector 45 located at theproximal end of the acceleration sensor unit 44. In one embodiment, theinsulator 49 of the elongate body 41 is an implantable polyurethane,silicone rubber or other implantable flexible polymer. At the distal endof the acceleration sensor unit 44, the electrical conductors 43, 47connect with the cardiac motion sensor 42. At the proximal end of theacceleration sensor unit 44, the electrical conductors 43, 47 connectwith the connector 45. Standard electrical bipolar or unipolarconnectors may be used as the connector 45, which provides mechanicaland electrical connections to the electronic device 22. The electricalconductors 43, 47 transmit the signal indicative of cardiac wall motionfrom the cardiac motion sensor 42 to the electronic device 22.

In accordance with the present invention, a preferred embodiment of thecardiac motion sensor 42 is constructed as an accelerometer that isparticularly sized for incorporation within a vein of a cardiac wall ofthe heart 100. In another embodiment, the cardiac motion sensor 42 isconstructed as an accelerometer that is particularly sized forincorporation in an implantable lead within a vein of a cardiac wall ofthe heart 100. Suitable accelerometers include, for example, theminiaturized accelerometer provided by Ball Semiconductor Inc. (see U.S.Pat. No. 6,197,610) and others that has a diameter of approximately 1millimeter. The cardiac motion sensor 42 can be an accelerometer formedby any available technology such as piezoelectric, piezoresistive,capacitive, inductive, or magnetic. The cardiac motion sensor 42 detectsand measures cardiac wall motion and provides a signal representative ofcardiac wall acceleration to the electrical conductors 43, 47 which thentransmit the signal to the electronic device 22.

FIG. 3 illustrates an implantable lead 26 incorporating a guide element60 and an acceleration sensor unit 44 in accordance with the presentinvention. The implantable lead 26 comprises a cylindrical lead 34 witha conductor used for sensing cardiac electrical activity and deliveringstimulation to the cardiac wall. The cylindrical lead 34 isconcentrically encompassed by a second cylindrical lead 30 possessing asimilar conductor, and the cylindrical lead 34 has an inner lumen 28.The conductor of the cylindrical lead 34 and second cylindrical lead 30may be an electrically conductive metal, as known in the art, formedinto an insulated coil configuration such as the Guidant EASYTRAK lead,or in other configurations such as a woven conductor. Moreover, thecylindrical lead 34 and second cylindrical lead 30 may have tapereddistal ends.

The implantable lead 26 is adapted to receive a guide element 60 alongthe inner lumen 28 of the implantable lead 26 for stiffening and shapingthe implantable lead 26 during the insertion of the implantable lead 26into the heart 100. Preferable guide elements include, for example,standard percutaneous transluminal coronary angioplasty guide wires.Once the guide element 60 is used to position the implantable lead 26within the heart 100 or veins of the heart 100, the guide element 60 isremoved from the inner lumen 28 of the implantable lead 26.

In an embodiment of the present invention, acceleration sensor unit 44is passed through the inner lumen 28 extending along the longitudinalaxis of the implantable lead 26 after the implantable lead 26 ispositioned within the heart 100, such as within the coronary sinus 110.The acceleration sensor unit 44 is extended into the implantable lead 26to optimally position the cardiac motion sensor 42 of the accelerationsensor unit 44. For example, the sensor 42 may be positioned adjacent tothe left atrium chamber 102 or left ventricle chamber 104 of the heart100. Once an optimal position for the cardiac motion sensor 42 isachieved, the acceleration sensor unit 44 is fixed relative to thelongitudinal axis of the inner lumen 28 of the implantable lead 26 byconnecting connector 45 to the electronic device 22. In this embodiment,the connector 45 may be disconnected from the electronic device 22, andthe acceleration sensor unit 44 may be removed from the inner lumen 28of the implantable lead 26 without removing the implantable lead 26 fromthe heart 100.

FIG. 4 illustrates the steps representing a method into which thepresent invention may be incorporated. At Step 200, a guide element 60is inserted along the inner lumen 28 of an implantable lead 26. At Step205, the implantable lead 26 is introduced into the heart 100, such aswithin the coronary sinus vein 110 of a cardiac wall. At Step 210, theimplantable lead 26 is positioned within the heart 100, such as withinthe coronary sinus vein 110, using the guide element 60. At Step 215,once the implantable lead 26 has been sufficiently positioned within theheart 100, the guide element 60 is removed from the inner lumen 28 ofthe implantable lead 26. At Step 220, the acceleration sensor unit 46 isinserted along the inner lumen 28 of the implantable lead 26.Subsequently, should it be necessary, the acceleration sensor unit 46may be removed from the lead 26 while the lead 26 remains installed inthe heart 100.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various other changes in the form anddetails may be made therein without departing from the spirit and scopeof the invention.

1. A method of detecting and measuring cardiac contractile functionsusing a signal representative of cardiac wall movement provided by anacceleration sensor, said method comprising the steps of: introducingsaid acceleration sensor unit into a vein of a cardiac wall, wherein thestep of introducing said acceleration sensor unit into said vein of saidcardiac wall comprises the steps of introducing an implantable lead intosaid vein of said cardiac wall and then inserting said accelerationsensor unit along an inner lumen of said implantable lead; positioningsaid acceleration sensor unit in said vein of said cardiac wall in amanner such that said acceleration sensor unit responds to movement ofsaid cardiac wall and provides said signal representative of cardiacwall movement; and connecting said acceleration sensor unit to anelectronic device.
 2. The method of claim 1, further comprising the stepof removing said acceleration sensor from said vein of said cardiacwall.
 3. The method of claim 1, wherein said vein of said cardiac wallis the coronary sinus vein.
 4. The method of claim 1, wherein saidelectronic device is an implantable cardiac resynchronization device. 5.The method of claim 1, further comprising the step of removing saidacceleration sensor from said vein of said cardiac wall.
 6. The methodof claim 1, further comprising the step of removing said accelerationsensor from said inner lumen of said implantable lead while a distalportion of said implantable lead is located within said vein of saidcardiac wall.
 7. A method of detecting and measuring cardiac contractilefunctions of a heart using a signal representative of cardiac wallmovement provided by an acceleration sensor, said method comprising thesteps of: inserting a guide element along an inner lumen of animplantable lead; introducing said implantable lead into said heart;positioning said implantable lead within said heart using said guideelement; removing said guide element from said inner lumen of saidimplantable lead; and subsequent to removing said guide element,inserting said acceleration sensor unit along said inner lumen of saidimplantable lead.
 8. The method of claim 7, further comprising the stepof removing said acceleration sensor from said inner lumen of saidimplantable lead.
 9. The method of claim 7, further comprising the stepof connecting said implantable lead and said acceleration sensor unit toan electronic device.
 10. The method of claim 7, wherein saidimplantable lead includes one or more electrodes.
 11. The method ofclaim 10, wherein said acceleration sensor unit is disposed adjacent tosaid electrodes.
 12. The method of claim 7, wherein said implantablelead is positioned within a vein of a cardiac wall of said heart. 13.The method of claim 7, wherein said implantable lead is directlyattached to a cardiac wall of said heart.
 14. A method of creating asensor for detecting and measuring cardiac contractile function, saidmethod comprising the steps of: inserting a cardiac motion sensor alongan inner lumen of an implantable lead; and positioning said cardiacmotion sensor within said inner lumen of said implantable lead such thatsaid cardiac motion sensor remains mobile relative to the longitudinalaxis of said implantable lead.
 15. The method of claim 14, furthercomprising the step of removing said cardiac motion sensor from saidinner lumen of said implantable lead.
 16. The method of claim 14,wherein said cardiac motion sensor comprises an accelerometer.
 17. Themethod of claim 14, wherein prior to inserting said cardiac motionsensor along said inner lumen of said implantable lead, said methodfurther comprises the steps of: connecting a conductor to said cardiacmotion sensor; passing said conductor through said inner lumen of saidimplantable lead; and connecting said conductor to an electrical devicesuch that said conductor fixes said cardiac motion sensor relative tothe longitudinal axis of said lead.
 18. The method of claim 17, furthercomprising the step of removing said cardiac motion sensor from saidinner lumen of said implantable lead.
 19. The method of claim 14,wherein prior to inserting said cardiac motion sensor along said innerlumen of said implantable lead, said method further comprises the stepsof: inserting a guide element along the inner lumen of said implantablelead; introducing said implantable lead into a vein of a cardiac wall;positioning said implantable lead within said vein using said guideelement; and removing said guide element from said inner lumen of saidimplantable lead.
 20. The method of claim 19, further comprising thestep of removing said cardiac motion sensor from said inner lumen ofsaid implantable lead.
 21. The method of claim 14, wherein prior toinserting said cardiac motion sensor along said inner lumen of saidimplantable lead, said method further comprising the step of attachingthe implantable lead directly to a cardiac wall.